1. Field of the Invention
The present invention relates to a substrate for a liquid discharge head and to a liquid discharge head.
2. Description of the Related Art
A liquid discharge head has a liquid discharge head substrate having on a silicon board an energy generation element configured to generate energy used to discharge liquid, and a flow path wall member forming the wall of a discharge port and of a flow path, and constructed by bonding thereof to the liquid discharge head substrate.
The energy generation element as mentioned above is formed by a heat generation resistor layer consisting of a heat generation material configured to generate heat through supply of electricity and by a pair of electrodes provided so as to be in contact with the heat generation resistor layer, and is covered with an insulation layer for protection from liquid. By applying voltage between the pair of electrodes, the heat generation resistor layer, disposed between the pair of electrodes, generates heat. Through this heat generation, the liquid causes film boiling to bubble, and is discharged through the discharge port by the pressure of a bubble generated at this time, whereby recording operation is performed.
It is known that, to protect the insulation layer, a protective layer having an anti-cavitation property consisting of a metal material or the like is provided on the insulation layer. As discussed in Japanese Patent Application Laid-Open No. 11-334075, an insulation layer consisting of a silicon compound is provided on the energy generation element, and a protective layer consisting of tantalum is provided thereon.
However, in recent years, to achieve an improvement of recording image quality and durability, a solvent of high degree of solubility is used as the liquid to be discharged, so that, depending on the kinds and concentrations of the components of the liquid to be discharged, the silicon layer consisting of a silicon compound may be dissolved, resulting in exposure of the electrodes to allow the liquid to be brought into contact with the electrodes.
Then, electric current will flow through a portion where it is not expected to flow, resulting in an unstable recording operation. It might be possible to cope with this problem by changing the material and thickness of the insulation layer. In reality, however, that would be very difficult when considering the characteristics related to the discharge performance, such as heat conductivity from the energy generation element to the liquid.